Lighting of light-emitting elements such as LEDs (Light Emitting Diodes) is usually controlled using a dynamic lighting system. The dynamic lighting system is a lighting system that sequentially scans a plurality of light-emitting elements by a predetermined number at a time and controls individually lighting and extinguishing the predetermined number of scanned light-emitting elements within the scanning period. For instance, when the total number of light-emitting elements is nine, these nine light-emitting elements are sequentially scanned three at a time, and the lighting and extinguishing the three scanned light-emitting elements within the scanning period are controlled individually.
A lighting control circuit that controls the lighting of light-emitting elements by means of such a dynamic lighting system has the advantage of being able to reduce the number of signal lines used for controlling the lighting of light-emitting elements. Due to this advantage, the lighting control circuit is provided in various types of equipment, apparatuses, and other objects. For example, an image forming apparatus such as a copy machine, a printer, a facsimile machine, or a multifunction machine equipped with the functions of these devices is provided with the foregoing lighting control circuit for controlling the lighting of the LEDs provided in an operation unit operated by a user. Note that the following PTLs 1 to 7 each disclose a conventional lighting control circuit that controls the lighting of an LED by means of the dynamic lighting system.
As described above, the lighting control circuit that controls the lighting by means of the dynamic lighting system has the advantage of being able to reduce the number of signal lines used for controlling the lighting of each light-emitting element. However, due to the tendency that the number of signal lines required for controlling the lighting increases as the number of light-emitting elements increases, when there are too many light-emitting elements (e.g., approximately several tens or more), even the lighting control circuit that controls the lighting by means of the dynamic lighting system ends up having too many signal lines.
Now, let it be assumed that the number of scanning signals (scanning signal lines) used for scanning light-emitting elements in the foregoing lighting control circuit that controls the lighting by means of the dynamic lighting system is n1, and that the number of lighting control signals (the number of lighting control signal lines) for controlling lighting and extinguishing the individual light-emitting elements within the scanning periods is n2. The maximum number of light-emitting elements whose lighting can be controlled by this lighting control circuit is defined by the product of these numbers (n1×n2). The number of signal lines used for controlling the lighting of these (n1×n2) light-emitting elements is the sum of these numbers, (n1+n2).
For example, in a case where the number of scanning signal lines is three (n1=3) and the number of lighting control signal lines is three (n2=3), the lighting of a maximum of nine light-emitting elements can be controlled. Specifically, a total of six signal lines are required in order to control the lighting of the nine light-emitting elements. However, in a case where the number of scanning signal lines is three (n1=3) and the number of lighting control signal lines is nine (n2=9), the lighting of a maximum of twenty-seven light-emitting elements can be controlled. Specifically, a total of twelve signal lines are required in order to control the lighting of the twenty-seven light-emitting elements, resulting in an increase of the total number of signal lines.